Ford Explorer, Maintaince And Repair Manual

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may want to take a moment to draw some pictures, or fabricate some labels or containers to mark the locations
of various components and the bolts and/or studs which fasten them. Modern day engines use a lot of little
brackets and clips which hold wiring harnesses and such, and these holders are often mounted on studs and/or
bolts that can be easily mixed up. The manufacturer spent a lot of time and money designing your vehicle, and
they wouldn't have wasted any of it by haphazardly placing brackets, clips or fasteners on the vehicle. If it's
present when you disassemble it, put it back when you assemble, you will regret not remembering that little
bracket which holds a wire harness out of the path of a rotating part.
You should begin by unbolting any accessories still attached to the engine, such as the water pump, power
steering pump, alternator, etc. Then, unfasten any manifolds (intake or exhaust) which were not removed
during the engine removal procedure. Finally, remove any covers remaining on the engine such as the rocker
arm, front or timing cover and oil pan. Some front covers may require the vibration damper and/or crank
pulley to be removed beforehand. The idea is to reduce the engine to the bare necessities of cylinder head(s),
valve train, engine block, crankshaft, pistons and connecting rods, plus any other 'in block' components such
as oil pumps, balance shafts and auxiliary shafts.
Finally, remove the cylinder head(s) from the engine block and carefully place on a bench. Disassembly
instructions for each component follow later in this section.
Cylinder Head
There are two basic types of cylinder heads used on today's automobiles: the Overhead Valve (OHV) and the
Overhead Camshaft (OHC). The latter can also be broken down into two subgroups: the Single Overhead
Camshaft (SOHC) and the Dual Overhead Camshaft (DOHC). Generally, if there is only a single camshaft on
a head, it is just referred to as an OHC head. Also, an engine with an OHV cylinder head is also known as a
pushrod engine.
Most cylinder heads these days are made of an aluminum alloy due to its light weight, durability and heat
transfer qualities. However, cast iron was the material of choice in the past, and is still used on many vehicles.
Whether made from aluminum or iron, all cylinder heads have valves and seats. Some use two valves per
cylinder, while the more hi−tech engines will utilize a multi−valve configuration using 3, 4 and even 5 valves
per cylinder. When the valve contacts the seat, it does so on precision machined surfaces, which seals the
combustion chamber. All cylinder heads have a valve guide for each valve. The guide centers the valve to the
seat and allows it to move up and down within it. The clearance between the valve and guide can be critical.
Too much clearance and the engine may consume oil, lose vacuum and/or damage the seat. Too little, and the
valve can stick in the guide causing the engine to run poorly if at all, and possibly causing severe damage. The
last component all automotive cylinder heads have are valve springs. The spring holds the valve against its
seat. It also returns the valve to this position when the valve has been opened by the valve train or camshaft.
The spring is fastened to the valve by a retainer and valve locks (sometimes called keepers). Aluminum heads
will also have a valve spring shim to keep the spring from wearing away the aluminum.
An ideal method of rebuilding the cylinder head would involve replacing all of the valves, guides, seats,
springs, etc. with new ones. However, depending on how the engine was maintained, often this is not
necessary. A major cause of valve, guide and seat wear is an improperly tuned engine. An engine that is
running too rich, will often wash the lubricating oil out of the guide with gasoline, causing it to wear rapidly.
Conversely, an engine which is running too lean will place higher combustion temperatures on the valves and
seats allowing them to wear or even burn. Springs fall victim to the driving habits of the individual. A driver
who often runs the engine rpm to the redline will wear out or break the springs faster then one that stays well
below it. Unfortunately, mileage takes it toll on all of the parts. Generally, the valves, guides, springs and
seats in a cylinder head can be machined and re−used, saving you money. However, if a valve is burnt, it may
be wise to replace all of the valves, since they were all operating in the same environment. The same goes for
any other component on the cylinder head. Think of it as an insurance policy against future problems related
to that component.
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452 Cylinder Head